The present invention relates to the manufacture of ophthalmic products. In particular, the invention provides molds for forming ophthalmic products, and methods for forming the molds and ophthalmic products using the molds.
The use of ophthalmic lenses, including spectacle lenses, contact lenses, intraocular lenses, and the like for the correction of ametropia is well known. Production of the lenses requires the use of molds that impart the desired corrective characteristics onto the lens surfaces. Typically, a large inventory of molds is required corresponding to each sphere, add, and cylinder power, and combinations thereof desired for the finished lens. Production and maintenance costs for the mold inventory are high.
One current method of forming contact lenses is actually by a process that has two molding steps. In the first molding step, male and female metal inserts, fabricated by such methods as diamond point turning to ensure a very smooth surface, are used to injection mold an ophthalmic lens mold comprising a pair of mold members, typically male and female plastic molds, also referred to as back curve and front curve lens molds. Then, in the second molding step, the contact lens forming material is dosed between the back curve and front curve lens molds and the contact lens is molded between the plastic back and front curve. Typically the back and front curves are not reused. The production of an ophthalmic lens mold typically comprising mold members in which a lens forming material is molded to form an ophthalmic product, is the subject of the present invention.
The injection molding step just described to form the ophthalmic lens mold members limits the types of materials that can be used to form the lens molds.
One method for production of lenses that attempts to eliminate the need for large inventory molds is disclosed in U.S. Pat. No. 6,026,204. In this patent is disclosed the use of customized, heated dies, which utilize mechanical fingers, alone or in combination with a metal surface, to impart the desired corrective characteristics to a lens blank. This method is disadvantageous in that it is unsuitable for the production of certain ophthalmic lenses, such as soft contact lenses because soft contact lens materials are thermoset that cannot be deformed with heat. Additionally, this method is disadvantageous in that molding the lens material using a heated die requires that the lens blanks"" optical axis be perfectly aligned with that of the die, which adds a great degree of difficulty to production of the lens. Therefore, a need exists for a method to produce ophthalmic lenses with a mold that permits reduction of lens inventory and which overcomes some or all of these disadvantages.
Shape memory polymers (SMPs) were developed about 20 years ago and have been the subject of commercial development in the last 10 years. SMPs derive their name from their inherent ability to return to their original xe2x80x9cmemorizedxe2x80x9d shape after undergoing a shape deformation. SMPs that have been preformed can be deformed to any desired shape below or above their glass transition temperatures (Tg). If it is below the Tg, this process is called cold deformation. When deformation of a plastic occurs above its Tg, the process is denoted as warm deformation. In either case the SMP must remain below, or be quenched to below, its Tg, while maintained in the desired thermoformed shape to xe2x80x9clockxe2x80x9d in the deformation. Once the deformation is locked in, the polymer network cannot return to a relaxed state due to thermal barriers. The SMP will hold its deformed shape indefinitely until it is heated above its Tg, whereat the SMP stored mechanical strain is released and the SMP returns to its preformed state.
Several polymer types exhibit shape memory properties. Probably the best known and best researched polymer type exhibiting shape memory properties is polyurethane polymers. Gordon, Proc of First Intl. Conf. Shape Memory and Superelastic Tech., 115-120 (1994) and Tobushi et al., Proc of First Intl. Conf. Shape Memory and Superelastic Tech., 109-114 (1994) exemplify studies directed to properties and application of shape memory polyurethanes. Another known polymeric system, disclosed by Kagami et al., Macromol. Rapid Communication, 17, 539-543 (1996), is a class of copolymers of stearyl acrylate and acrylic acid or methyl acrylate. Other SMP polymers known in the art include articles formed of norbornene or dimethaneoctahydronaphthalene homopolymers or copolymers, set forth in U.S. Pat. No. 4,831,094, incorporated herein by reference.
In accordance with the present invention, an ophthalmic mold comprising a shape memory polymer (SMP) or shape memory alloy (SMA) is provided. The mold preferably comprises at least two mold members, preferably two mold members, of which at least one mold member comprises a SMP or SMA. The mold preferably comprises a front curve and a back curve, and is preferably used to form a contact lens; however, the ophthalmic products that may be formed using the ophthalmic molds of this invention include spectacle lenses, contact lenses, interocular lenses or the like.
Additionally, this invention provides a molding surface of an agile tool or as referred to in U.S. Ser. No. 09/649,635, a deformable mold comprising a SMP or SMA; however, the focus of the description will be the formation of an ophthalmic mold comprising an SMP or SMA; however, the teachings herein can be applied to the molding surface of the agile tool.
The mold of this invention comprising an SMP or SMA can be used to make a lens and then re-shaped and re-used to form another lens, thereby reducing the amount of mold material consumed in a lens manufacturing facility. Additionally in alternative embodiments, the molds formed by the methods described below can be used to produce more varied contact lenses and even customized contact lenses at a lower cost than if metal inserts had to be fabricated to make each mold member. Additionally, by using the mold of this invention in manufacturing ophthalmic products, a mechanical demold step, used in the prior art to remove an ophthalmic product molded within the mold, may be eliminated and replaced with the step of heating the mold comprising a SMP or SMA above its Tg to cause the mold to deform, at which time the ophthalmic product can be removed from the mold without the mechanical demold step.
Further, the molds of this invention are not formed by injection molding at high temperature, i.e. as high as 300xc2x0 C., and elevated pressure, thereby providing new types of materials that can be used to make the devices, that shape the ophthalmic molds. By forming molds by methods other than injection-molding, different mold forming materials, and methods can be used to make the molds. Additionally, if the agile tools described herein are used to make the molds a full prescriptive range of lenses can be produced while reducing the number of molds required, and eliminating all the injection-molding tools required to do the same. Further, the molds of the invention may be used in a method for the delivery of customized ophthalmic lenses to a lens wearer.